Bread toasters are known which--apart from the actual tasting process of a toasting item introduced through a loading and unloading opening into the toasting chamber of the bread toaster--likewise permit to warm up items outside of the toasting chamber. To this end, the item to be warmed up is placed on a retaining means which is mounted on the top of the bread toaster above the loading and unloading opening (see e.g. German utility model No. 69 04 032). When the object is being warmed up, no toasting item is in the toasting chamber, whereby the warm air emitting from the toasting chamber and the infrared radiation generated therein by a heating device may reach via the loading and unloading opening the object to be warmed up that lies on the retaining means.
The warming-up time for the respective item to be warmed up is adjusted in the known bread toaster by the same means as is the toasting time for a roll to be toasted. In the majority of the known bread toasters, the completion of the toasting process is performed by a mere time control and often by using bimetal elements (see e.g. DE-PS 178 53 119). The user of the toaster adjusts the time on the basis of pragmatical values acquired in practice.
Beside the use of bimetal elements, it is known already to perform the time control electronically in bread toasters according to the species. Thus, the magazine "Siemens-Components" 22 (1984) volume 1, pages 18 to 21 (see herein pictures 22 and 23 and the pertinent description) teaches already to use a programmable digital long-term timer (Siemens type model SAB 0529) which, by way of an integrated coded switch, permits to adjust toasting times ranging between thirty seconds and four minutes. The commencement of the toasting process is determined in that, after the manual start-up of the bread toaster, the long-term timer keeps two contacts closed by means of a magnet, the said contacts providing connection between the heating device and its voltage supply. Upon termination of the set toasting time, the magnet will be de-energized again by the long-term timer for concluding the toasting process, in consequence whereof the two contacts will re-open and the heating device will be separated again from its voltage supply.
Besides, a bread toaster is known (see DE-AS 15 15 042) permitting the user to directly set the desired toasting degree of the object being toasted instead of a toasting time found by experience. Upon attainment of this toasting degree, the toaster is set out of operation automatically irrespective of the toasting time. For controlling the toasting process, this known bread toaster comprises a sensor responsive to the infrared radiation which it is receiving as it emanates from the surface of the item being toasted, and which delivers a sensor signal derived therefrom to a comparator circuit, thereby disabling the bread toaster via a switch step when a predeterminable signal level is attained.
It is easily possible to improve upon this known comparator circuit to such extent that it allows to adjust various signal levels for the sensor signal that it allows to adjust various signal levels for the sensor signal and thus various toasting degrees, upon attainment of which the comparator circuit will issue a respective toasting-time control signal switching the bread toaster off.
When it is desired with a like sensor-equipped bread toaster to warm up an item placed outside of the toasting chamber on top of the loading and unloading opening of the bread toaster, there is the following difficulty:
Since the toasting chamber of the bread toaster does not contain an item to be toasted, the sensor receives an infrared radiation which meets it directly emitting from the heating device. Due to the fact that the temperature of the heating device, on start-up of the bread toaster after a short start-up time, ranges between 800.degree. and 1000.degree. C., while the toasting process of an item to be toasted will be interrupted already when the latter reaches a temperature of roughly 160.degree. C.--even in the event of a maximum signal level being adjusted--, the sensor will issue after a short time already such a large sensor signal that the heating device of the bread toaster is set out of operation. However, the resulting relatively short operating time of the bread toaster is not sufficient to warm up an object placed on top of the loading and unloading opening of the bread toaster to the extent desired.
Therefore, it is an object of the present invention to devise a bread toaster in such a fashion that the operating time of the bread toaster, with the toasting chamber empty, is not controlled by the infrared radiation received by the sensor and hence is too short, but that the operating time of the bread toaster in this case is extended sufficiently long for the purpose of entirely warming up an item to be warmed up which is placed outside of the toasting chamber on top of the loading and unloading opening.